---
title: Item identifier and duplicates
slug: pb5g3451
canonical_url: https://docs.coveo.com/en/pb5g3451/
collection: index-content
source_format: adoc
---
# Item identifier and duplicates
During [content update operations](https://docs.coveo.com/en/2039/), the [Coveo Platform](https://docs.coveo.com/en/186/) must uniquely identify [items](https://docs.coveo.com/en/210/) already [indexed](https://docs.coveo.com/en/204/) and avoid creating duplicates.
Coveo uses the `uri` [field](https://docs.coveo.com/en/200/) value to distinguish items.
To see an item's `uri` value, inspect its [properties](https://docs.coveo.com/en/2053#content-browser-features) in the [**Content Browser**](https://platform.cloud.coveo.com/admin/#/orgid/content/browser/) ([platform-ca](https://platform-ca.cloud.coveo.com/admin/#/orgid/content/browser/) | [platform-eu](https://platform-eu.cloud.coveo.com/admin/#/orgid/content/browser/) | [platform-au](https://platform-au.cloud.coveo.com/admin/#/orgid/content/browser/)).

![an item uri in the Content Browser | Coveo](https://docs.coveo.com/en/assets/images/index-content/item-uri-in-properties.png)

The sudden appearance of duplicates in your index may indicate that the `uri` [field](https://docs.coveo.com/en/200/) value of items has changed between two content update operations.
This article explains how item URIs are derived and provides troubleshooting guidance to identify and resolve item URI-related issues.

## How `uri` field values are derived

Like all Coveo fields, the `uri` field is populated using [metadata](https://docs.coveo.com/en/218/) extracted from your content.
The way that metadata is extracted depends on the source type used to index your content.

With many source types, the source automatically extracts the metadata required to populate the `uri` field, for example, the item's URL.

With other source types, metadata extraction is manual: you must specify in the source configuration which piece of information from your content to extract as the metadata for the `uri` field.
For example, a Database source requires you to specify the item URI metadata value syntax in the text node of the [`<Uri>` element](https://docs.coveo.com/en/l15b4451#uri-required) in the source's XML configuration.
To make the content of the `<Uri>` element unique for each item, it must include a dynamic value, such as a reference to the `ID` column, as shown in the following example:

```xml
<Uri>http://www.example.com/Customers/details.aspx?Id=%[ID]</Uri>
```

## Troubleshooting item URI issues

Given the [different ways sources populate item URI metadata](#how-uri-field-values-are-derived), either automatically or through user-defined expressions, the root cause of duplicate items can vary.

With sources where the metadata extraction is automatic, the root cause is usually in your content or in the way your system presents the content.
For example, if the metadata used to populate the `uri` field changes from `example.com/my item` to `example.com/my%20item` due to a space character encoding change, Coveo won't recognize it as the same item.
This results in both versions appearing in your index instead of just the updated one.

With sources where you configure metadata values manually, the issue may stem from:

* Changes to the URI metadata value expression in the source configuration.

* Changes to the dynamic values used in the URI metadata value expression.

In either case, the simplest way to resolve duplicate item issues is to remove all source items from your index and repopulate it from scratch.
When the source type supports it, use a source [rebuild](https://docs.coveo.com/en/2712/) to do so.

With Push sources, perform a [`Delete old items`](https://docs.coveo.com/en/131/) and then re-push all your content to the index.

With Catalog sources, perform a full rebuild using either the [load operation](https://docs.coveo.com/en/p4eb0129#load-operations) or the [update operation](https://docs.coveo.com/en/p4eb0129#update-operations).
If you use the update operation, ensure you [remove the old items](https://docs.coveo.com/en/p4eb0129#step-4-delete-old-items).